The invention relates to a high temperature furnace for generating high temperature gases as are needed for use in such applications as soda ash processes, smelting, and drying. The invention is applicable to furnaces adapted to burn solid fuels having an ash content such as coal, dried sewage sludge and like materials.
It is well known that solid organic material such as coal typically contains inorganic minerals and the like to the extent of several percent of its weight. When the material is pulverized and burned, these inorganic minerals form a finely divided ash. At temperatures below 2,000.degree. F., the ash is entrained in the gas stream in the form of particles which may be removed by conventional electrostatic precipitation methods. When the furnace is operated above 2,400.degree. F., the ash becomes molten slag, precipitates on the furnace walls, and can be withdrawn through a tap in the bottom of the furnace so long as it is maintained at a sufficiently high temperature. If the slag is allowed to solidify prior to its removal from the furnace, the tap may become clogged, thereby necessitating shutdown of the furnace and costly repairs.
U.S. Pat. No. 3,947,001 shows an arrangement having a downdraft vertical furnace with a slag removal tap at the bottom. An auxiliary burner, typically gas or oil fired, maintains the slag in its molten state. Such a burner requires a second fuel capacity, which is inefficient, cumbersome, and expensive.